To form a lead frame for an encapsulated semiconductor device the lead frame is mechanically stamped or chemically etched from a piece of metal such as copper or copper alloy. During stamping, the edges of the metal, for example the metal around lead fingers, can become burred, rounded, and otherwise misformed due to tearing or shearing of the metal. This can make attachment of a bond wire to a lead finger less reliable and more difficult than with a properly shaped, flat and nonburred lead finger.
To reduce the problems associated with burred, rounded, and narrow lead fingers, a lead frame can be coined at the lead fingers in the area where a bond wire is to be connected. This effectively flattens and widens the tips of the lead finger to provide a flat surface for the connection of the bond wire. Coining allows for a decreased pitch with etched lead frames as it widens the bonding surface, and is therefore desirable with etched lead frames as well. With a leads-over-chip (LOC) assembly, the side of the lead finger opposite the coining is connected to a circuit side of the semiconductor die, then the bond wires are formed to electrically couple the semiconductor die with the lead fingers.
Coining the lead fingers, however, can create various problems. As a result of the tips of the lead fingers being coined, a step-like discontinuity is created on the surface to which the bond wire is to be attached. The bond wire must be carefully positioned so as to avoid placing the bond at this discontinuity, which would result in a weak attachment of the bond wire to the lead finger.
A semiconductor assembly which avoids problems associated with coined lead frames of previous designs would be advantageous.